In CUCM, navigate to “Cisco Unified Serviceability -> Tools -> CDR Analysis and Reporting -> CDR ->Export CDR/CAR”.
NOTE – it may be in CUCM12 that one of those options above takes you over to the Unified Administration page.
Set the end of the timerange as close as you can to the moment when the real-time data first started coming in (this is to minimize any gap or overlap).
Use that page to download the file. You’ll get one very large CDR file, and if call diagnostics are enabled, also a CMR file.
Rename those 2 files so that they’re prefixed cdr_and cmr_respectively (and make sure the prefixes are lowercase cdr and cmr).
The easiest thing to do is to simply drop those files into the same directory being watched by the sinkhole data input. Despite the file being so much larger than the ones that come in in real-time, the file contents will get indexed, and the file itself deleted by the sinkhole input.